staging: dgap: remove unnecessary function

The dgap_init_global() initialize the dgap_board
that is a global variable as static and dgap_poll_timer.
But init_timer() is called twice in dgap_start() and dgap_board
doesn't need to be initialized to NULL.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>